Polyphenylquinoxalines (PPQ) are condensation polymers commonly synthesized by the reaction of bis(.alpha.-diketones) with aromatic bis(o-diamines) and having a repeat unit of the general type ##STR1## Ar is a tetravalent aromatic radical which can be as simple as 1,2,4,5-tetrasubstituted benzene. Ar may be a bis(o-diphenylene) having the general structure ##STR2## where X=nil, O,S,SO.sub.2,C.dbd.O, etc., or Ar may be any other appropriate tetravalent radical. Ar' is a divalent aromatic radical which may be 1,3-phenylene, 1,4-phenylene, 4,4'-biphenylene, 4,4'-oxydiphenylene, 4,4'-thiodiphenylene, 4,4'-carbonyldiphenylene, 4,4'-methanediphenylene, or any other appropriate divalent radical.
Synthesis and characterization of polyphenylquinoxalines has been extensively reported in the literature. The initial report was in 1967 [P. M. Hergenrother, J. Polym. Sci. A-1, 5, 1453 (1967)] with a patent awarded in 1973 [J. M. Augl and W. J. Wrasidlo, U.S. Pat. No. 3,766,141 (Oct. 16, 1973) (to U.S. Navy)]. A review on polyphenylquinoxalines was published in 1971 [P. M. Hergenrother, J. Macromolecular Science-Reviews in Macromolecular Chemistry, C6(1), 1(1971)]. For the most part the Ar' part of the bis(.alpha.-diketones) is wholly aromatic. This is desirable if exceptionally high thermal stability is required, but glass transition temperatures tend to be high (more than 250.degree. C.) and processing temperatures much higher (more than 300.degree. C.). Little research has been attempted to significantly reduce the processing temperatures of polyphenylquinoxalines.
The incorporation of a flexibilizing segment such as an aliphatic or an alkylenedioxy group into the repeat unit of an aromatic/heterocyclic polymer is an effective means of reducing the glass transition temperature and improving processability. Ethylenedioxy groups have been incorporated into the main chain of polyimides [W. A. Feld et al., J. of Polym. Sci. Polymer Chem. Ed., 21, 319(1983); F. W. Harris et al., Polymer Preprints, 25(1), 160(1984); and F. W. Harris et al., Ibid., 26(2), 287(1985)]. Significant reductions in glass transition temperatures and increased melt flow at elevated temperatures were observed.
Polyphenylquinoxalines are more readily prepared than polyimides, not requiring elevated temperatures for ring closure. It would therefore be useful to incorporate into polyphenylquinoxalines some flexibilizing alkylenedioxy segments in such a manner as to reduce glass transition temperature and improve processability while not significantly reducing the excellent mechanical properties. P. M. Hergenrother [J. Polym. Sci., Part A-1, 6, 3170(1968)] reported the synthesis of two polyphenylquinoxalines containing hexylene linking groups in the Ar' segment. Characterization of these polymers was limited to inherent viscosities and determination of polymer decomposition temperature in air and nitrogen. There was no mention of glass transition temperatures or processability of these polymers. Thus, the use of flexibilizing groups in polyphenylquinoxalines has not been fully utilized.
The flexibilizing alkylenedioxy unit could be incorporated into either the Ar [bis(o-diamine)] or the Ar' [bis(.alpha.-diketone)] portion of the polyphenylquinoxaline repeat unit. In either case the synthesis of the new monomers containing the flexible segment would require several steps for preparation from commercially available materials.
A primary object of the present invention is to provide new polyphenylquinoxalines that are useful as adhesives, coatings, films, membranes, and composite matrices.
Another primary object of the present invention is the synthesis of five new monomers, the 4,4'-(.alpha.,.omega.-diphenoxyalkyl) bis(phenylethanediones), where .alpha.,.omega. represent terminally substituted alkanes containing two to six carbon atoms.